Possibly the most confusing intersection in Washington County, a choppy “sea of pavement” where thousands of drivers struggle daily to navigate it will undergo a major reconstruction this spring and summer.

Twelve lanes of traffic converge at a sprawling four-way stop at Manning Avenue and 10th Street, leading to dangerous encounters of swerving vehicles.

“Nobody’s sure what to do in an intersection that large,” said Washington County traffic engineer Frank Ticknor.

Work begins in May on the $3.4 million project, including two new traffic signals, rebuilt roads, and improvements such as a bike path and sidewalk. The County Board on Tuesday approved a construction contract with Valley Paving, Inc., for work that Ticknor said will be completed before school starts in the fall.

Parents driving students to nearby Oak-Land Junior High School have expressed concern about heavy traffic through the intersection, as have administrators. School District 834 will contribute $50,000 to the project for improvements and a traffic signal at the school’s south entrance.

A second traffic signal will be installed at the main intersection.

The county is involved because both major thoroughfares are county roads — 10th Street is County Road 10, and Manning Avenue is County Road 15. Thousands of commuters use both routes, which slice through Lake Elmo and West Lakeland Township.

Traffic has increased substantially in recent years, Ticknor said. In 2000, the portion of Manning Avenue south of the intersection saw about 11,000 vehicles a day, but that number grew to 15,700 in 2015. On 10th Street, 4,000 vehicles a day in 2000 jumped to 5,300 in 2015.

“We’ve been targeting that intersection for a long time,” Ticknor said, because it ranked as one of the county’s worst.

A banked portion of Manning at the intersection will be graded flat because vehicles traveling on 10th Street, at faster speeds through a new green light, might otherwise go airborne, he said.

Additional funding will come from the city of Lake Elmo, which under the county agreement will pay $38,000 for the bike path and sidewalk.

Ticknor said drivers can use the north-south Manning route during construction, but he said east-west 10th Street will be closed intermittently throughout the summer.

Washington County “has committed significant resources” this year to road and bridge projects, said Commissioner Fran Miron, who chairs the board.